I'm not sure why Aerith is so memorable to a lot of people (let alone the characters in the game itself. Of course, though, no matter how long I was with someone, I'd be sad if they were such a good person and died tragically). I knew about her death before I played the game, but it still caused some pain for me (same with Elmyra's story, and Cait Sith #1's death.) Perhaps some people didn't know anyone died in this game, or they didn't think Square would choose her to fill the Matyr's roll. Perhaps it's also because, while she is not perfect in any sense, she was still one who could be labeled "innocent"...